Network telephone voice enhancement services are provided "in-line" with transmission facilities. These services are incorporated in thinks which are in turn connected between switching systems, because such services cannot otherwise be added into the circuit. An illustration of this system may be seen in the example of FIG. 1, wherein a long distance network is shown. Telephone 101 is connected to a local switch 102, which is, in turn, connected to an originating long distance switch 103 by access trunk 104. Originating switch 103 is connected to a terminating switch 105, via trunk 106. The terminating switch is connected to a local exchange carrier switch represented by 108. The call is completed to telephone 109. As can be seen in this figure, there are two echo cancelers, 110 and 111, connected between originating switch 103 and terminating switch 105, on trunk 106. Echo canceler 110 cancels echoes of telephone 101, and echo canceler 111 cancels echoes from telephone 109. Other voice enhancement facilities, such as AT&T's True Voice .RTM. voice enhancement services are also connectable to trunk 106 in order to further enhance the sound of the voice signal.
There are, however, several drawbacks to the configuration of FIG. 1. First, failures in these in-line enhancement circuits require that the trunk be taken out of service, which may cause calls to be lost. For example, any failure in either echo canceler 110 or 111, or both, will cause trunk facility 106 to be lost. The result is that fewer long distance calls can be completed between switch 103 and switch 105, and, if the failure occurs during an active call, may result in the call being torn down. Second, all circuits are routinely tested, which means that in order for switch 103 to test echo canceler 110, it must take trunk 106 out of service, and further, must alert switch 105 that it is doing so. Switch 105 must cooperate in the test of echo canceler 110 and report back to switch 103. The same scenario holds true when switch 105 tests echo canceler 111. Further, new voice enhancement features cannot economically be introduced until all trunks incorporating the new feature are connected to a particular switch, since 100% deployment is required to guarantee that the enhancement is available for all calls.
Additionally, long distance companies are now entering the interlata telephone service market by connecting telephone calls between local switches in the same service area. So, for example, in FIG. 1, when telephone 101 connected to local switch 102 calls telephone 112 connected to local switch 114, instead of connecting through a trunk connected between the local exchange carrier switches or, alternatively, connecting through a tandem operated by the local exchange carrier, the user at telephone 101 may cause the call to be connected through switch 103 instead.
In such cases, the telephone service provider that owns switch 103 would like to be able to offer enhanced services which differentiate from the local exchange carrier. To this end, it is desirable to have voice enhancement services and features on access trunks 104 and 118. However, in order to provide such voice enhancement features, the telephone service provider that owns switch 103 must have the cooperation of the local exchange carrier in order to routinely maintain such services in line on access trunks 104 and 118. Such cooperation may be difficult to obtain when the service providers are in competition for the same telephone traffic.
Therefore, a problem in the art is that there is no system for adding voice enhancement circuits other than building them in-line with trunks.